An exhaust-gas cooling device of the above type is known from DE 10 2004 019 554 A1. In the embodiment illustrated in the document, the hot exhaust gas is first is fed into a so-called heat exchanger, and the heat exchanger comprises ribs extending in the flow direction and intended to provide an improved heat transition between the exhaust gas and the coolant. During the flow of the exhaust gas through this heat exchanger, the heat exchanger will be susceptible, along with the increasing temperature of the exhaust gas, to sooting and char depositions so that the flow through the heat exchanger will be impeded. The sooting tends to occur particularly in the return flow path of the U-shaped heat exchanger because, in that stretch of the path, the exhaust gas has already been considerably cooled. In an effort to accomplish an improved heat transition while at the same time reducing the sooting, further prior art documents, e.g. DE 20 2006 009 464 U1, have proposed to select a special arrangement of the ribs and/or a special shape of the ribs. However, none of these approaches have been found useful for basically preventing the sooting throughout the operating life of the heat exchanger.
Thus, it is an object of the invention to provide an exhaust-gas cooling device which is adapted to still further reduce the sooting in the heat exchanger unit, while effecting the reduction at the lowest possible expenditure for production and the lowest possible costs.